1. Field of the Invention
The present invention relates in general to a carbon diffusion surface hardening process, and in particular to a pack carburization process for carburizing the surface of 300-series stainless steel.
2. Description of the Related Art
The use of surface hardening diffusion processes in increasing the wear resistance of metal alloys is well established and has been in commercial use for many years. Several common surface hardening diffusion processes in commercial use include pack carburizing, gas carburizing, carbo-nitriding, and nitriding. In these processes, carbon and/or nitrogen are diffused into the surface of the metal alloy.
Surface hardening is used to produce a hard wear-resistant surface without affecting the soft, tough, core properties of the alloy. This combination allows the maufacture of wear-resistant parts with good impact resistance. Generally, inexpensive low carbon low-alloy steels or ferritic stainless steels are used for producing surface hardened parts. These steels depend on the austenite to ferrite (.gamma..fwdarw..alpha.) phase transformation and the carbon and/or nitrogen diffused into the surface for their wear resistance.
U.S. Reissue Pat. No. 29,881 describes a method of vacuum carburizing metal articles which include a sintered stainless steel. U.S. Pat. Nos. 4,533,403 and 4,495,006 describe methods for borocarburizing ferrous substrates. U.S. Pat. No. 4,495,005 describes a process for carbosiliconizing ferrous substrates. U.S. Pat. No. 4,539,053 describes a pack composition method for carburosiliconizing ferrous substrates.
The carburization of 300-series stainless steels is universally believed to be detrimental to the series corrosion properties. The formation of chromium carbides generally result in reduced corrosion properties under normal alloy usage conditions, though increases surface hardness.
Thus, there is a need for a surface hardening process for increasing the wear resistance of 300-series stainless steels, where the environment is not conducive to detrimental corrosive attack, but where other beneficial properties of austenitic stainless steels (eg. oxidation resistance, creep strength) may be used to advantage.